NTSB Identification: GAA15LA22514 CFR Part 91: General AviationAccident occurred Friday, July 31, 2015 in Peoria, AZProbable Cause Approval Date: 01/21/2016Aircraft: ULTRAMAGIC N250 - NO SERIES, registration: N57EXInjuries: 1 Serious, 10 Uninjured.NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.The pilot reported that, during the balloon deflation process after landing and when the balloon was about 90 percent deflated, a wind gust caught the fabric that still had hot air trapped in it. The basket subsequently tipped forward, and one passenger slid out of the basket and sustained a serious injury. The pilot reported no preaccident mechanical malfunctions or failures with the balloon that would have precluded normal operation.The National Transportation Safety Board determines the probable cause(s) of this accident as follows:The pilot's failure to ensure that the passengers remained secure in the basket during deflation after landing, which resulted in a passenger falling out of the basket and sustaining a serious injury when a wind gust caught the envelope and tipped the basket on its side.On July 31, 2015 about 0750 mountain standard time, an Ultramagic SA N250 balloon, N57EX, tipped over during the deflation process after landing in an open field in Peoria, Arizona. The pilot and nine of the ten passengers were not injured. One passenger sustained serious injuries. The balloon sustained no damage. The balloon was registered to the Mars-Leasing Company, Inc. of Phoenix, Arizona, and was operated by Hot Air Expeditions, Inc. of Phoenix, as a day, visual flight rules, passenger flight under 14 Code of Federal Regulations, Part 91. Visual meteorological conditions prevailed at the time of the accident and no flight plan was filed. The flight originated from private property in Phoenix, and was conducted in the local area.According to the pilot, the accident occurred during the deflation process after landing. The pilot reported that, "all passengers were in landing positions and were advised to stay in their landing positions." When the balloon was approximately 90 percent deflated, a gust of wind caught the fabric that still had trapped hot air. The basket tipped forward and one passenger slid out of the basket. The passenger sustained serious injury. The injured passenger reported that she was briefed by the pilot after the landing that the balloon "may tip" and that she was holding onto the basket. The pilot reported no mechanical malfunctions or failures with the balloon prior to the flight that would have resulted in abnormal operation of the balloon.